Colored images are often used in medical applications. For example, conjunctival redness has important value in the evaluation of ocular inflammatory or surface disease. Conjunctival redness can be assessed subjectively based on a physician's clinical criteria. Clinicians can guide their criteria using sets of photographs, of which there are different versions and none is considered as a standard. Evaluating conjunctival redness by simple visual observation, whether based on images or direct in-person observation, introduces subjectivity and thus a potential source of bias.